Multiple plate throttling orifice



' 0 United States Patent 11113,545,492

[72] Inventor Charles H. Scheid, Jr. [56] References Cited Middletown,Ohio UNITED STATES PATENTS [21] l 3*12 1,078,834 11/1913 Cook 48/180[221 e 3,111,091 1 H1963 Hopkinson 13s/44x [45] Patented Dec. 8,1970FORE N P TEN S [73] Assignee Armco Steel Corporation [G A T Middletown,Ohio 520,083 4/1940 Great Britain 138/40 3 corporafion of Ohio PrimaryExaminer-Laverne D. Geiger Assistant Examiner-R. J. SherAttorney-Melville, Strasser, Foster and Hoffman ABSTRACT: A throttlingdevice for hydraulic systems which prevents the cavitation of metalconduits by liquids under dif- [54] MULTIPLE PLATE THROTTLING ORIFICEferential pressure comprising a series of orifice plates spaced 7claimss Drawing Figs at intervals along the axis of the conduits, eachplate having [52] U.S. Cl. 138/42, n or r rifi s her in t lower thepressure of the liquid 138/44 passing therethrough, the axes of theorifices being displaced [5]] 1115.] 1/02 radially and circumferentiallyabout the plate centers so as to [50] 138/42, 44; be in l m n i h he xef he rifi es in adjacent modate water must allowfor MULTIPLE PLATErrmorrunc onmce BACKGROUND OF THE INVENTION ferentialpressure.

2. Description ofthe lemma.

Hydraulic systems such as thosefound on presses and the like havegenerally heretrifo're utilized oil' as the hydraulic .medium, andthrottle valves, such as globe-type throttle valves, have provedgenerally satisfactory. Due to the fact that -oil as the hydraulic fluidis relatively dangerous, many newer,

hydraulic systems have. adopted water rather than oil as the hydraulicfluid. However, the cavitation problem is much greater with watersincethe vapor pressure of oil is lower than that of water. Also, sincehydraulic oils are more compressible than water and thus exhibit moredeflection under thesame pressure, the design of conduits and othervessels to accoma greater dissipation of energy through the walls. I r

By cavitation is meant the gradual erosion of a surface caused by thecollapse of vapor bubbles in a fluid. These bubble's form whenthestaticpressure in a fluid is lowered to the vapor pressure of the fluid.When the bubbles collapse the fluid slaps the surface, causing a'smallpart of the surface to be stressed beyond its yield point. Thiseventually results in fatigue and pitting of the surface. 7 v iCavitation, of course, causes frequent shutdowns of hydraulic systems sothat new valves may be installed. The shutdowns become very expensive interms of man hours of maintenance because of the general inaccessibilityof the valves.

Prior art devices have offered no solution to this problem. Indeed, theprior art'does not seem to even recognize the cavitation problem. Forexample, U.S. Pat, No. l,078,834,'in the'name of Cook, disclosesafgaseous fuel mixer which cornprises a numberofagitating plates withina tubular housing.

The plates arefmounted on'ashank and may be rotated to properly mix thegas flowing therethrough. Each of the plates has a number of apertures,the number of apertures increasing from the first to last plate, withrespect to the flow, while the size of the apertures decreases as thenumber of holes increasesfiCookdoes not'indic'ate that the rotatingorifice plates are to serve any other purpose than to properly mix thegaseous fuel. l b b j Another exemplary prior art patent U.S. Pat. No.2,125,245

. in the name of McCray,.which discloses an apparatus fordispersingthermoplastichydrocarbon materials in water. The

are positioned between the dispersing plates and are formed 7 withrestricted passages through which the materials being dispersed arepassed. McCray makes no mention of the cavitation problem. I

The aforementioned references are simply exemplary of prior artteachings which disclose multiple orifice plates. The references are notconcerned with the problem of cavitation and its prevention, andthemultiple orifice plates are primarily used to mix various materialspassing therethrough.

SUMMARY or Tris INVENTION The present invention. provides a throttlingdevice for hydraulic systems which prevents the cavitation of metalconduits by liquids under differential pressure. Broadly speaking,

therethrough, and the axes of the orifices-are displaced radiallyandcircumferentially about the plate centers so as to be in FIG. 1.

misalignment with the axes of the orifices in adjacent plates. Thisprevents the jet leaving one orifice plate from entering directly anorificein an adjacentplate. The orifice, plates are positioned such thatthe upstream plate provides the greatest pressure drop thereaCt'OSS andeach succeeding plate provides a gradually decreasing pressure drop,whereby the static pressure in the liquid under differential pressure isat all points greater than the vapor pressure of the liquid.

The spaced intervals between orifice plates will preferably be such asto allow the most length for dissipation where the pressure drop isgreatest, so that the flow entering thenext orifice plate will be asundisturbed as possible. I

In practice, the throttling device of the present invention will preventthe cavitation of metal conduits by any liquid under differentialpressure. However, since in practice it has been found that cavitationis much more serious when water is utilized as the hydraulic fluid, thepresent invention will be most applicable in this connection. I

In a preferred embodiment, the number of orifice plates was found to befive."The first four orifice plates were provided with sharp edgeorifices and thelastorifice plate was a short tube orifice type.

BRIEF DESCRIPTION OETHE DRAWING FIG. 1 is a cross section taken throughthe center of a multiple plate throttling orifice according to thepresentinvention.

FIG. 2 is an end elevation of the multiple plate throttling orifice ofFIG. g

FIG. 3 is a cross-sectional view. taken along the line 3-3v of FIG].

FIG. 4 is a cross-sectional view taken along the line 4-4 of FIG. 5 is across-sectional view taken along the line 5-5 of FIG. 1.

FIG. 6 is a cross-sectional view taken along the line 6-6 of FIG. 7 is across-sectional view taken along the line 7-7 of FIG].

FIG. 8 is a cross-sectional view taken along the line 8-8 of DESCRIPTIONOF THE PREFERRED EMBODIMENTS As was previously explained, the cavitationproblem is much greater when water is used as a fluid in an hydraulicsystem than when oil is used as the fluid. This is so because theorifice of this invention. This throttling device was designed toreplace an existing globe-type throttle valve and to throttle.

water, which was used as the hydraulic fluid, to slightly aboveatmospheric pressure.

For purposes of explanation, the multiple plate throttling device 10 ofthis invention is heldwithina housing 12 having a from 4,200 p.s.i.

bore 12a therein. The housing 12 may join two conduits in a hydraulicsystem. It is, of course, obvious that the throttling device 10 of thisinvention maybe used in any hydraulic system where it is desired tothrottle the flow across a large pressure drop and where cavitation is aproblem.

The housing 12 hasbeen designed ,such that both the upstream anddownstream ends thereof have flanged connections which permitthem to bejoined to other sections of com duit by bolts and the like through thebolt holes 12c.

As can be seen from FIG l,the multiple plate throttling orifice of thisinvention comprises a series of orifice plates 13 through 17 which areseparated by the spacers 18 through 21.

.therethrough. The axesof the orifices in each of the plates 14 through17 are displaced radially and circumferentially about the respectiveplate centers so as to be in misalignment with the axes of theorificesinadjacentplates. This preventsthe jet leaving one orifice plate, theupstreamplate, from entering directly an orifice in an adjacentdownstream plate.

It will be observed that the orifice plates 13 through 17 are positionedsuch .that. the upstream plate 13 provides the greatest pressuredropthereacross and ,each succeeding plate provides a graduallydeereasingpressure drop. In this manner the static pressureinthe quidunder differential pressure is at all points greater than the vaporpressure of the liquid.

It is, of course, well =know n that for a single orifice plate the flowrate Q is equal to CA*?"2g (Ah), where C is the coefficient ofdischarge, which is a combination of a velocity coefficient C,,) and acontraction coefficient (C A is the total cross-sectional area of theorifice, g is the coefficient for gravity, and Ah is the difference inhead upstream of the orifice and downstream at the vena contracta. Thevelocity head which is recovered is equal to the standardorifice-differential pressure (Ah in the above formula) minus the nethead loss due to me- ,tering; Thus, the static pressure at the venacontracta is less than the static pressurefurther downstream and will infact decrease towards a staticpressure reading of zero. In actualpractice, the sta'tic pressure atthe vena contracta may not belowerthanthe-vapor pressure of the liquid, because once this V happensabubble forms and cavitation occurs.

Since theabove formula is for a single orifice ,plate, and the presentinventionutilizes a number of orifice plates in series, a certaindesired flow rate was assumed. This flow rate and the elevated positionof {the fluid system utilizing this throttling device, a hydraulicpress, resulted in a certain inherent back head. The area of theorifices in the furthest downstream orifice plate was determined so thatthe static pressure at the vena contracta, taking into a'ccounttheinherent back head and the velocity head recovered, was above the vaporpressure of the liquid. The area of the orifices in the next orificeplate upstream was then determined in the same manner using the inherentback head plus the'rret head loss due to metering of the 'farthestdownstream orifice. The total pressure 'drop across'the multiplatethrottling orifice plates could then be calculated as the sumof the netheadloss due to metering for each orificeplate. It was then necessary tomake several iterations of the whole calculation until the totalcalculated pressure drop for the throttling device was equal to theavailable pressure drop supplied by thehydraulic system, at which timethe initially assumed flow rate was proved;

As may be seen from FIG. 1 and FIGS. 4 through 8, all but the lastorifice platefhav'e' sharp edge orifices while the last plate is of theshort tube orifice type. Appropriate orifice coefficients. were used foreach in the aforementioned calculations/However, it should be'emphasizedthat the type of orifice which is ultimately selected'is merely a matterof design so long as'the appropriate orifice coeff cients are utilizedin the aforementioned calculations.

It should be pointed out that. the number of orifices in each orificeplate is not important, only their total area. Thus plates withmultiplate holes were considered as having a single hole,

the area of which was equal to the sum of the area of the multipleholes. The reason for using multiple holes and their specific locationwas to prevent the jet leaving one orifice plate from entering directlya hole in the next plate.

Obviously, if the static pressure ofthe liquid at any point in thehousing is too close to the vapor pressurethereof, some cavitation willoccur. It then becomes necessary to increase the number of orificeplates.

The distance between the orifice plates 13 through 17,

established by the spacers 18 through 21; has not been found .10 becritical..However, it has been found preferable to allow ,themost lengthfor dissipation where the pressure drop is -the greatest in order thatthe flow entering the next orifice plate will beas'undisturbed aspossible.

.vals along the axes of said conduits each plate having one or moreorifices therein to lower the pressure of the liquid passingtherethrough, the axesof said orifices being displaced radially andcircumferentially about the plate centers so as to be in misalignmentwith the axes of the orifices in adjaceirt plates and to prevent the jetleaving one orifice plate from entering directlyan orifice in anadjacentplate, the total area 'of said orifices in each succeeding orirce plateon the downstream side being successively larger so that the u'pstreamplate provides the greatest pressure drop thereacross and eachsucceeding plate provides a gradually decreasing pressure drop, wherebythe static piessure in said liquid under differential pressure is at allpoints greater than the vapor pressure of said liquid.

' and to ensure that the flow entering the next adjacent orifice platewill be as undisturbed as possible.

3. The throttling device according to claim 1, wherein the total area ofthe orifices in each'on'fice plate is determined so that the minimumstatic pressure between said orifice plates is above the vapor pressureof the fluid according to the formula Q Ca**2g (8h), where Q is the fidwrate, C is the coefficient of discharge and is a combination of avelocity coefficient and a contraction coefficient, A is the totalcross-sectional area of the orifice, g. is the coefficient for gravity,and 8h is the difference in head upstream of the orifice plate anddownstream UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PatentNo. 3,5 6,492 Dated December 8, 1970 Inventorfl!) CHARLES H. SCHEID, JR.

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

Column 3, Line 22, please amend "CA 2g 11)" to read CA V 2g (Ah) Column3, Line 2 4, please amend "C to read --(C Column 4, Line 50 in claim 3,please amend "Ca 2g (811)" to read --CA 2g (Ah Column 4, Line 53, inclaim 3, please cancel "811" and insert Ah SEALED 161971 (SEMI Am Mummun. swam. an.

more mine:- at We

